预制钻孔煤样冲击倾向性及能量耗散规律

Bursting liability and energy dissipation laws of prefabricated borehole coal samples

  • 摘要: 基于煤的冲击倾向性测定方法进行预制钻孔煤样单轴加载试验,研究钻孔煤样的冲击倾向性变化规律,引入破碎颗粒分形维数与新增表面积,分析钻孔煤样破碎过程中的能量耗散规律。结果表明:① 钻孔使试样以剪切劈裂破坏形式转变为在孔洞两侧孕育、融合裂隙并在岩桥之间产生贯穿裂纹的破坏形式,同时伴随塌孔现象。随钻孔排数增多,钻孔试样呈现出应力峰前塑性损伤逐渐增大,峰值强度降低、积聚弹性能减少,峰后破坏耗时延长、耗能提升的趋势,且单轴抗压强度、冲击能量指数、弹性能量指数均逐渐降低,动态破坏时间显著升高,冲击倾向性逐渐减弱。② 试样破碎颗粒分形维数与新增表面积具有良好的负相关性:试样破碎程度越低,分形维数越高,新增表面积越小。③ 试样应力峰前能量的输入、耗散与新增表面积无明显关系。峰后能量释放及耗散规律与破碎颗粒新增表面积变化规律一致,新增表面积越大则峰后耗能越多。受加载速率及钻孔布置影响峰后能量差值与新增表面积变化呈“U”形变化趋势。钻孔减缓了试样峰后能量释放与能量耗散速率,且二者降低幅值较为相近,单孔试样降低约 17.0%,双孔试样降低约68.3%,三孔试样降低约 70.8%。钻孔卸压可以降低峰前积聚的应变能,降低峰后单位时间内释放的能量,使得不易发生动力破坏。

     

    Abstract: Uniaxial loading test of pre-drilled hole samples was carried out based on the measurement methods of bursting liability of coal to study the mechanical properties and bursting liability of samples.Combined the fractal dimension and the newly added surface area of broken particles,the energy dissipation characteristics of coal samples during different drilling arrangements were analyzed.The results show that the drilling makes the failure form of the sample change from shear splitting to a failure form of gestation and fusion of cracks on both sides of the hole,and form through cracks between the rock bridges,accompanied by collapse.As the number of drill holes increases,the drilled samples show a gradual increase in pre-peak plastic damage,and gradual decreases both in the peak strength and the accumulated elastic energy,the post peak damage reflects the trend of prolonged time consuming and increased energy consumption.The uniaxial compressive strength,the bursting energy index and elastic strain energy index are both significantly reduced,the duration of dynamic fracture is significantly increased,and the bursting liability is reduced.The fractured particle fractal dimension is negatively correlated to the newly added surface area,the lower the degree of fragmentation of the sample,the higher the fractal dimension,the smaller the newly added surface area.The input,dissipation of energy before the stress peak of the sample have no obvious relationship with the newly added surface area.The law of energy release and dissipation after the peak of the samples are consistent with the distribution law of the newly added surface area of the crushed particles.The larger of the newly added surface area,the more energy consumption after the peak.Affected by loading rate and drilling layout,the energy difference after the peak and the new surface area change show a U shaped change trend.Drilling slows the rate of post peak energy release and energy dissipation of the sample,and the reduction amplitudes of the two are relatively similar.The single hole sample reduces by about 17.0%,the double hole sample reduces by about 68.3%,and the three hole sample reduces by about 70.8%.The test results show that borehole pressure relief reduces the accumulated strain energy before the peak,and reduces the energy release per unit time after the peak,making the sample less prone to dynamic damage.

     

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